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Q.Integrate: ∫xtan⁡−1x(1+x2)3/2 dx\displaystyle\int \dfrac{x\tan^{-1}x}{(1+x^2)^{3/2}}\,dx

Odisha ChseOdisha CHSE +2 Science Board Exam 2022Subjective· 5mImportance★★★★★
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Recognize that x(1+x2)−3/2x(1+x^2)^{-3/2} is (up to sign) the derivative of (1+x2)−1/2(1+x^2)^{-1/2}, so use integration by parts with u=tan⁡−1xu=\tan^{-1}x and that piece as dvdv.

Let I=∫xtan⁡−1x(1+x2)3/2 dxI=\displaystyle\int\dfrac{x\tan^{-1}x}{(1+x^2)^{3/2}}\,dx.

Notice ddx[−11+x2]=x(1+x2)3/2\dfrac{d}{dx}\left[-\dfrac{1}{\sqrt{1+x^2}}\right]=\dfrac{x}{(1+x^2)^{3/2}}, so take dv=x(1+x2)3/2dxdv=\dfrac{x}{(1+x^2)^{3/2}}dx, giving v=−11+x2v=-\dfrac{1}{\sqrt{1+x^2}}; and u=tan⁡−1xu=\tan^{-1}x, so du=dx1+x2du=\dfrac{dx}{1+x^2}.

Integration by parts, I=uv−∫v duI=uv-\int v\,du:

I=−tan⁡−1x1+x2−∫(−11+x2)dx1+x2=−tan⁡−1x1+x2+∫dx(1+x2)3/2I=-\dfrac{\tan^{-1}x}{\sqrt{1+x^2}}-\int\left(-\dfrac{1}{\sqrt{1+x^2}}\right)\dfrac{dx}{1+x^2}=-\dfrac{\tan^{-1}x}{\sqrt{1+x^2}}+\int\dfrac{dx}{(1+x^2)^{3/2}}

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